Dielectric resonator (DR) filters are band pass filters for microwaves that provide an alternative to resonant cavity filters. A DR filter comprises a plurality of spatially separated dielectric resonators supported in an assembly, wherein the dielectric resonators are electromagnetically coupled. An electromagnetic wave is introduced into the assembly, and excites the resonators, producing a filtering resonance response in the filter that may then transmit a filtered signal.
Dielectric resonator filters are widely used in wireless base stations, satellites and other communications and space applications, due to their superior performance and miniaturization as well as their wide commercial availability. The use of DR filters in many applications is limited, however, because prior art DR filters are relatively expensive, and are not amenable to mass production.
There are two configurations of DR filters that are most commonly used in the art. In the first configuration, individual dielectric resonators are supported axially in a metallic enclosure, in which it is difficult to physically support the resonators. In the second configuration, individual resonators are mounted in a planar configuration. In the latter case, dielectric resonators are centered in position and mounted inside a filter housing using supports formed of a material having a low dielectric constant and a low loss. In some cases, such as in a triplet with negative cross-coupling, additional pins are required in the assembly for coupling.
The frequency response of a DR filter is dependent on the design of the resonators, and on the couplings between them. The couplings are dependent on the distance between the resonators. Thus, in a conventional DR filter design, any error in the placement of the dielectric resonators on the supports may have a significant effect on the performance of the filter.
The critical nature of the positioning of each resonator in a filter, and the number of separate components that must be assembled in a given filter, lead to a high cost of assembly, alignment and integration of the combined dielectric resonator and support structure, which becomes a major factor contributing to the overall cost of the DR filters. Grinding the individual resonators and machining the individual supports is another key factor in the overall cost of DR filters.
Therefore, there remains a need for a new DR filter that is suitable for low-cost mass production.